Lightning arrester



April 1, 1952 R. D. NELSON ETAL 2,591,370

LIGHTNING ARRESTEJR Filed March 29, 1951. 2 SHEETSSHEET 1 INVEN TORS.fiaflane/D A/6/60/1 ,4 Tram/.5 Y V April 1, 1952 R. D. NELSON ET AL2,591,370

LIGHTNING ARRESTER Filed March 29, 1951 2 SHEETS-SHEET 2 BY faw/n A L/nkATTOlP/VE'Y Patented Apr. 1, 1952 UNITED STATES PATENT OFFICE Link,Milwaukee, Wis., Transformer & Equipment 00.,

assignors to Rural Milwaukee,

Wis., a corporation of Illinois Application March 29, 1951, Serial No.218,232

14 Claims.

This invention relates to electrical discharge devices, or lightningarresters, for preventing excess voltages or high potential currentsurges in the power line, caused by lightning, atmospheric or otherconditions, from flowing into the load lines carrying electricalinstrumentalities which might be severely damaged thereby. The generalpurpose of lightning arresters. connected to electric transmission anddistribution lines are two-fold; first, to discharge excessive voltagesproduced by lightning or other causes; and second, to interrupt the flowof follow up currents through the arrester upon the return of the systemto a normal voltage.

Many forms of lightning arresters have been used, embodying variousprinciples of operation, in attempts to provide devices which wereintended to afford successful repeated operation without being destroyedor severly damaged.

However, most of these devices have failed to prove entirelysatisfactory either because of failure in service or from the standpointof costliness due to complexity of construction.

This invention is designed to overcome the above noted defects byproviding a new and improved lightning arrester, which, due to itssimple construction, will afford a device capable of repeated efiicientand effective operation in discharging excessive voltages orhigh-potential current surges and providing means for extinguishing thearc, formed during the operation of the device, by the process ofdeionization which precludes the flow of follow up currents through thelightning arrester upon the return of the system to a normal operatingline voltage.

The primary object of the present invention resides in the provision ofa new and improved lightning arrester, including essentially a pair ofspaced electrodes and a dielectric structure formed of gas evolvingmaterial and providing a means for confining a discharge arc. Thedielectric structure is so constructed as to effeet the initialestablishment of a discharge spark along a restricted path and then,through the action of the evolved gases generated by the establishedarc, effect the transfer of the discharge are to another less restrictedpath of travel having a greater length but offering less resistance thanthat encountered along the initial shorter restricted path of travel ofthe discharge are due to the increased resistance caused by the presenceof the evolved gases. The longer path of travel serving to confine thedischarge are within a passage wherein it is extinguished through theprocess of deionization brought about through the expending force of theevolved gases upon the arc stream.

Another object of the invention resides in the provision of a new andimproved lightning arrester including essentially a pair of electrodesand a dielectric structure formed of gas evolving material forming ameans for confining a discharge arc and including means for venting thedevice to alleviate the possibility of rupture of the lightning arresterunder the influence of pressure built up as the result of the gasesformed by the presence of the arc in the process of discharging thehigh-potential current surges in the power line.

Another object of the invention resides in the provision of a new andimproved lightning arrester including an intermediate electrodepositioned in spaced relationship with the line electrode on one sideand the ground electrode on the other side, in a manner to afford aseries arrangement of the air gaps, including one which is substantiallyunconfined and a second air gap which is confined within the dielectricstructure.

Another object of the invention resides in the provision in a new andimproved lightning arrester of a dielectric structure arranged toconfine a spark gap and provide a plurality of paths which the dischargespark may follow including one path adapted, by reason of its length andlow resistance, for the initial establishment of the discharge spark andan additional path, of predetermined length greater than the other path.to which the discharge spark is transferred when the resistance to theflow of the discharge spark in the initially established path of travelis increased, under the action of the deionizing gas formed as theresult of the discharge sparks action on the dielectric structure whichis formed of gas evolving material, to a value which is greater than theresistance offered in the additional path of travel having apredetermined greater length.

Another object of the invention resides in the provision in a new andimproved lightning arrester of a dielectric structure formed of gasevolving material and comprising a plurality of members arranged forcooperative association to provide a confined chamber in which adischarge spark is established and further providing a plurality ofpaths along which the discharge spark may travel, one of the pathsoffering negligible resistance to the establishment of the dischargespark between the adjacent portions of the electrodes housed within thedielectric 3 structure and the other of the paths being of apredetermined length greater than the lower resistance path. The shorterof the alternate paths is partially restricted while the longer oneforms a continuous unrestricted passage for the discharge arc.

Another object of the invention resides in the provision of a new andimproved dielectric structure forming an essential part of the lightningarrester; the dielectric structure including a plurality oftelescopically arranged members formed of gas evolving material andcooperating in a manner to provide a plurality of paths for a dischargeare; one of the paths being shorter and more restricted than the other.The shorter path offering less resistance to the establishing of thedischarge are and the longer path offering an unrestricted passagewithin which the discharge are is extinguished by the process ofdeionization through the action of the evolved gases which increase theresistance to the flow of the discharge arc along its initiallyestablished path of travel to an amount greater than the resistance toits flow through the longer unrestricted passage to which it transfersand in which it is extinguished through the expending force of theevolved gas upon the arc stream.

Another object of the invention lies in the provision of a new andimproved lightning arresterincluding an improved form of dielectricstructure formed and arranged in a manner such that they cooperate todelineate separate paths of travel for the flow of a discharge arc; oneof the paths being partially restricted and shorter in length than theother path which is unrestricted and formed by a groove in one membercooperating with the wall of another member.

Another object of the invention resides in the provision of a new andimproved lightning arrester incorporating a dielectric structure formedof a plurality of members composed of vulcanized fibre or other gasevolving material and including a pair of tubular members and a spiralmember. These members are constructed in a manner to permit their nestedrelationship to form a dielectric structure adapted to delineate a pairof paths for a discharge spark; one path being along the surface of oneof the tubular members and being partially restricted by the proximityof the surface of the spiral member and the other of the paths beingunrestricted and formed by the adjacent convolutions of the spiralmember in cooperation with the adjacent walls of the tubular members.

A more specific object of the invention resides in the provision of anew and improved lightning arrester which is simple in construction,economical to produce and one which is adapted for repeated operationover a long period of time without fear of damage or the need ofreplacement.

Other objects and advantages will become apparent from the followingdescriptions of illustrative embodiments of the present invention.

In the drawings:

Figure 1 is an elevational view of a lightning arrester constructed inaccordance with the teachings of the present invention and adapted formounting upon a conventional cross arm bracket provided with a groundconnection;

Fig. 2 is an enlarged vertical sectional view showing the internalstructure of the lightning arrester illustrated in Fig. 1;

Fig. 3 is a horizontal sectional view. taken on the line 3-3 of Fig. 2,showing the upper electrode, the open chamber in which the discharge 4are can jump and venting means for relieving gas pressure formed in thechamber as a result of the formation of a high-potential discharge are;

Fig. 4 is a horizontal sectional view, taken on the line 4-4 of Fig. 2,showing the construction and arrangement of parts in the gas evolvingchamber forming the lower spark gap of the lightning arrester;

Fig. 5 is a horizontal sectional view, taken on the line 55 of Fig. 2,showing abutment means on the intermediate electrode which servesthrough contact with a portion of the dielectric structure to establishthe correct length of the lower spark gap;

Fig. 6 is a bottom plan view of the lightning arrester, removed from themounting bracket, showing venting means in the form of ports to relievepressure and prevent rupture of the arrester under the influence of thedeionizing gas generated as the result of the formation of ahigh-potential discharge are in the lower enclosed spark gap chamber;and

Fig. 7 shows a modified form of the dielectric structure comprising twogas evolving members constructed in a manner to form a plurality ofseparate paths along which a high-potential discharge are may flow; oneof the paths being shorter than the other and following a surface on oneof the members thus ofiering negligible resistance to the establishmentof a discharge arc;

while the other path is of a predetermined length substantially greaterthan the first mentioned path and delineated by a groove or passagewayformed between the two members of the dielectric structure.

Referring more particularly to Fig. 2 of the accompanying drawings, itwill be noted that the lightning arrester l0, chosen for illustrativepurposes and embodying the teachings of the present invention, comprisesa base casting H which serves to support a dielectric structure l2 and aconventional hollow porcelain housing element l3. The base casting I Iof the lightning arrester I0 is arranged for mounting in a conventionalmanner upon a cross arm mounting bracket 14 to support the device indesired operating position.

The functional portions 01' the lightning arrester II], which willhereinafter be more specifically described, are contained within orattached to the hollow porcelain housing element l2 and include ametallic line electrode IS, a metallic ground electrode 16, and anintermediate metallic electrode l1. These electrodes l5, l8 and I! areretained in spaced axial alignment within the lightning arrester II! toprovide a pair of air gaps l8 and I9 arranged in series relationship.The air gap It! being located between the adjacent portions of theelectrodes l5 and I1 while the air gap I9 is located between theadjacent portions of the electrodes l6 and H.

A brief description of the structural formation of the several parts ofthe lightning arrester ID will serve to simplify the understanding ofits assembly and mode of operation. The base casting ll formed ofcurrent conducting material such as a metal casting is cylindrical inshape and includes a flat bottom 20, an enlarged body portion 2|provided with an outwardly directed flange 22 and an upwardly extendingannular flange 23. The casting H has an axially disposed cored cavityincluding a machined bore 24 extending downwardly from the top of theflange 23 and terminating in a shoulder 25 from which a cavity 26 ofreduced diameter projects downwardly to surround a boss 21 having a flattop surface 28, positioned above the lower extremity of the cavity 26.The boss 21 contains a threaded bore 23, extending upwardly from thebottom surface of the casting H, adapted to receive a cap screw by whichthe lightning arrester I0 is anchored to the cross arm mounting bracketH. The boss 21 has a portion of its wall and top interrupted by a slot3| to provide open communication between the threaded bore 23 and thecavity 26 for a purpose to be hereinafter described. A series ofvertically disposed circumferentially spaced slots or openings 32 formedin the wall of the base casting II serve to vent the cavity 26 to theatmosphere. Another series of vent passages 33 in the form of axiallyarranged holes extending through the body portion 2| of the castingprovide means for relieving any pressure built up within the upperchamber of the lightning arrester III.

The dielectric structure l2, illustrated in Fig. 2 of the drawings,comprises a plurality of members, formed of vulcanized fibre or othergas evolving material, an inner tubular member 34 having an axiallydisposed center bore 35 and a smooth outer surface 36; an outer tubularmember 31 having an axial bore 38 provided with a threaded portion 39and terminating at its upper end in an enlarged bore 4|]; and a helicalmember 4|. The several members 34, 31 and 4| are constructed so thatthey may be telescopically arranged with the outer surface 42 of thehelical member 4| slidably receivable in the bore 38 of the outertubular member 31 and lying in close proximity thereto and with theouter surface 36 of the inner tubular member 34 slidably receivablewithin and lying in close proximity with the inner surface 43 of thehelical member 4|. The space between the adjacent upper and lowersurfaces of the helical member 4| cooperating with the outer surface 36of the inner tubular member 34 and with the bore 38 of the outer tubularmember 31 to delineate an unrestricted helical or spiral passageway 44between the lower extremity of the intermediate electrode l1 positionedin the threaded portion 39 of the bore 38 and the ground electrode I5disposed at the lower extremity of the outer tubular member 31 of thedielectric structure H.

In assembling the lightning arrester H], the ground electrode I6, whichis in the form of a metal washer, is inserted into the bore of a tubularmetal shield 45 which is closely fitted into the bore 24 of the basecasting II and serves to position the tubular member 31 of thedielectric structure l2 which is inserted into the metal shie d 45 andpressed downwardly until the ground electrode I6 is seated upon theshoulder 25 of the base casting II. The tubular member 31 of thedielectric structure I2 is retained in position within the metal shield45 by means of an anchoring pin 46 which is secured in aligned holes inthe member 31 and shield 45 to prevent relative movement of the partsunder the influence of the pressure of gas formed by the highpotentialdischarge are upon the gas evolving material of the dielectric structureduring the operation of the lightning arrester Ill. The helical member4| is then inserted into the bore 38 of the member 31 and positioned sothat its lower end is resting upon the upper surface of the groundelectrode I6. The inner member 34 of the dielectric structure I2 is theninserted into the helical member 4| and positioned with its lower end incontact with the top surface 28 of 6 E the boss 21 disposed within thecavity 26 in the base casting With the several parts of the dielectricstructure l2 properly positioned, the intermediate electrode I1 is thenthreaded into the portion 33 of the bore 38 to a position.in which theabutment portions 41 on the electrode l1 contact the upper extremity ofthe inner tubular member 34. The length of the member 34 is such thatthe desired length of the spark gap I9 is established between the lowerextremity of the intermediate electrode l1 and the top surface of theground electrode Hi.

The line electrode l5 which cooperates with the intermediate electrodeIT to form another spark gap I5 is rod-like in form and extendsvertically through a metal bushing 48 mounted in an opening 49 formed inthe top of the porcelain housing element 3. The lower portion of theline electrode l5 projects downwardly into a chamber 50 in the housingl3 while the upper threaded portion 5| of the electrode l5 extends abovethe top of the housing l3 to provide a means for securing a lineconnection terminal 52 in position on the housing. A sealing gasket 53serves to provide a tight connection between the terminal 52 and thehousing I3.

The housing I3 is positioned on the base casting II by placing theenlarged mouth 54 of the chamber 50 over the horizontally extendedflange 22 of the casting |l so that the shoulder, formed between thechamber 5|! and enlarged mouth 54, rests upon the top surface of theflange 22. With the dielectric structure l2 properly assembled andmounted on the base casting H and the line electrode l5 secured inposition in the porcelain housing element I3, the housing element maythen be secured in position on the base casting H by the application ofsuitable sealing material 55 to unite the parts of the lightningarrester I0 into a unitary structure.

The electrical connections to and from the lightning arrester |0comprise a power line lead 56 which connects the power line to theterminal 52 and a ground wire 51 which has one end connected to aconventional ground connector 53 secured to the cross arm mountingbracket l4 in the usual manner, and its other end grounded.

A description of the operation of the lightning arrester ID will serveto emphasize its simplicity and efiectiveness in discharginghigh-potential current surges in the power line, due to lightning orother causes, and in extinguishing the discharge are formed during itsoperation to prevent the establishment of follow up currents passingthrough the lightning arrester I0 upon the restoration of normalvoltages in the power line. The lightning arrester I0 is so constructedthat high-potential current surges occurring in the power line aretransmitted through the power line lead 56, the line terminal casting 52and the line electrode IS, the upper air gap l8 between the lower end ofthe line electrode l5 and the top of the intermediate electrode l1,thence through the intermediate electrode l1, the lower air gap l9between the bottom of the intermediate electrode l1, and the groundelectrode l6, through the base casting l l, the cross arm mountingbracket l4, and to the ground through the connector 53 and the groundwire 51; to thus discharge the excessive high-potential current.

It should be noted that the upper air gap I8 is located within theenlarged portion 40 of the bore 38 formed in the outer tubular member 31of the dielectric structure I2 and that the mouth of the bore 40 is inopen communication with the chamber 50 of the porcelain housing elementI! which in turn is connected to the atmosphere through the vent holes33. The venting of the chamber 50 serves to insure against rupture ordamage to the lightning arrester l resulting from the pressure generatedfrom the affect of the heat of the discharge are upon the gas evolvingmaterial of the dielectric structure 12 in the immediate proximity ofthe arc. It should also be noted that the relative positioning of theseveral parts of the dielectric structure I2 located between or adjacentthe pieces forming the lower air gap I9 is such that the initialestablishment of the discharge are across the gap l3 will follow thepath of least resistance which is substantially a straight line alongthe surface of the bore 38 between the bottom edge of the intermediateelectrode I1 and the top surface of the ground electrode I6. Thiscondition 01' least resistance to the flow of the arc in a substantiallystraight line along the surface of the bore 33 is promptly destroyedunder the efiect of the heat of the are upon the dielectric structurewhich evolves a gas that deionizes to materially increase the resistanceto the continued flow of the discharge arc along the initiallyestablished path of travel, due to the close proximity of the severalconvolutions of the helical member 4| with the surface 38 along whichthe discharge are was established. The increase in resistance to theflow of the discharge are along the initially established path of travelis substantially instantaneous and of sufficient magnitude to divert thedischarge spark to the longer path of travel defined by the helicalpassageway 44, the resistance of which is now less than that of theinitially established path of the discharge are. In this manner, thedischarge are is considerably lengthened and the gas evolved from thesurrounding dielectric members through the heat of the discharge arc issufllcient to deionize the atmosphere of the passageway 44 and effectthe extinguishing of the discharge are by the deionization processcoupled with the expending force of the gas under pressure which blowsthrough the passageway 44 and is vented to the atmosphere through theports 32 formed in the base casting I l. The venting of enclosed air gapl9 not only provides insurance against the rupture of the dielectricstructure l2 under the pressure generated within it by reason of thepresence of the discharge arc but further provides for the freecirculation of air through the air gap chamber to assist in the actionof extinguishing the discharge are under the expending force of thegenerated gas. The venting and circulating system permits the readyingress or egress of air to or from the cavity 26 by way of the seriesof openings 32 formed in the wall of the base casting ll. As will beseen from Fig. 2 of the drawings, air may pass from the cavity 26through the slot 3|, the bore 35 of the inner tubular member 34 andthence outwardly and downwardly between the inner surface of theintermediate electrode I1 and the outer surface 36 of the member 34;into the air gap I9 and thence through the central opening in the groundelectrode l6 and into the cavity 26, which is in open communication withthe exterior of the lightning arrester H! through the openings 32. Theestablishing of the discharge are in the passageway 44 builds upconsiderable pressure within the confines of the dielectric structureand causes a rush of generated gas along the path of travel of thedischarge spark with the result that the gas follows path of thedischarge spark through the passageway 44 in expending its force toassist in the lengthening of the discharge spark and in effecting itsextinguishment by the process of deionization within the passageway 44.Upon the extinguishment of the discharge arc, the entire chamber withinwhich the air gap I9 is located is in such condition that it resists theestablishment of a follow up current through the lightning arrester Illafter the reestablishment of the normal potential in the power line.

Referring more particularly to the modified form of the dielectricstructure shown in Fi 7 of the accompanying drawings, it will be notedthat the dielectric structure I! chosen for illustrative purposes iscomposed of an inner member BI and an outer member 62 both formed ofvulcanized fibre or other are extinguishing or gas evolving material. Inthis modified form, it will also be noted that the outer surface of theintermediate portion of the member 6| is provided with a helical groove63 which cooperates with an axial bore 64 in the outer member 62 to forma passage 65 or discharge are path having a predetermined length whichis substantially greater than a straight line are path along the innersurface of the outer member 62 which represents the path of thedischarge arc upon its initial establishment, when the modified form ofdielectric structure l2 replaces the structure l2 previously described.It should also be understood that the helical groove 53 or an equivalentformation might as well be formed in the outer member 62 of thestructure; or as a matter of fact, the groove 63 need not be of helicalform as its sole purpose is to provide a path for the discharge arcwhich has a predetermined length which is greater than the straight linedistance between the adjacent portions of the electrodes which form theair gap in which the dielectric structure is disposed.

From the foregoing description of the illustrativeembodiments of thepresent invention, it will be apparent that a new and improved lightningarrester has been provided which is adapted to function repeatedly andin rapid succession, if necessary, Without fear of damage to thearrester or without requiring attention or replacement of parts overyears of efiicient and effective service.

It should also be noted that the lightning arrester of the presentinvention, in addition to being simple in construction and relativelyinexpensive to manufacture, includes a new and improved dielectricstructure which provides a plurality of independent paths of travel forthe discharge arc; one for the initial establishment of the dischargespark and another to ,which the discharge spark may be automaticallytransferred and in which it may be more readily extinguished through theprocess of deionization to preclude the possibility of follow upcurrents passing through the lightning arrester after thereestablishment of the normal line potential after the dischargeoperation of the arrester is completed.

While the invention has been described in considerable detail, in theforegoing specification, it is to be understood that various changes maybe made in its embodiments without departing from or sacrificing any ofthe advantages hereinafter claimed.

We claim:

1. A lighting arrester comprising a line electrode, a ground electrode,an intermediate electrode disposed between and in spaced relationp withsaid other electrodes to form an air gap between it and each of saidother electrodes, and a dielectric structure formed of are extinguishingmaterial confining one of said air gaps, said dielectric structureincluding a plurality of paths of travel for a discharge spark bridgingsaid confined air gap, one of said paths of travel being shorter inlength, more restricted and offering less resistance to theestablishment of a discharge spark than the other of said paths oftravel, the establishment of a discharge spark in said shorter morerestricted path effecting an increase in resistance to its continuedtravel along said path of sufficient magnitude to divert the path oftravel of the discharge spark to said longer less restricted path oftravel wherein it is extinguished by the process of deionizaticn.

2. A lightning arrester comprising a plurality of metallic electrodesarranged in spaced relationship, said electrodes including a lineelectrode, a ground electrode and an intermediate electrode, saidelectrodes cooperating to provide a pair of air gaps arranged in series,and a dielectric structure formed of arc extinguishing materialconfining one of said air aps, said dielectric structure including aplurality of paths of travel for a discharge spark bridging saidconfined air gap, one of said paths of travel being shorter, morerestricted and offering less resistance to the establishment of adischarge are than the other of said paths of travel, whereby theinitial establishment of the discharge are in said shorter path oftravel is insured, the establishment of a discharge are in said shorterpath of travel effecting a marked increase in resistance to thecontinued flow of the discharge are by reason of the action of thedischarge spark upon the confining are extinguishing material and therestricted nature of said path, the increased resistance in theinitially established path of travel having sufficient magnitude toeffect the transfer of the discharge are to said longer, less restrictedpath of travel wherein it is extinguished by the process ofdeionization.

3. A lightning arrester comprising a plurality of metallic electrodesarranged in spaced relationship to provide a pair of air gaps, and adielectric structure formed of arc extinguishing material, saiddielectric structure confining one of said air gaps and providing aplurality of paths of travel for a discharge are bridging the confinedair gap, one of said paths being shorter than the other and offeringless resistance to the initial establishment of a discharge spark, theestablishment of the discharge spark effecting an increase in resistancealong said path of travel through the action of the discharge spark uponthe dielectric material to divert the discharge spark to said longerpath of travel then having a lower resistance wherein it is extinguishedby the process of deionization.

4. A lightning arrester comprising a plurality of metallic electrodesarranged in spaced relationship to provide a pair of air gaps in series,and a dielectric structure formed of are extinguishing materialconfining one of said air gaps and providing a pair of separate paths oftravel for a discharge are bridging said confined air gap, one of saidpaths of travel being shorter, more restricted and oifering lessresistance to the establishment of a discharge are between the saidelectrodes of said confined air gap to insure the initial establishmentof the discharge are in said shorter path, the establishment of thedischarge are in said shorter path effecting an increase in itsresistance to the continued flow of the discharge are through the actionof the discharge are upon said dielectric structure, said increasedresistance being of sufficient magnitude to exceed the resistance ofsaid other path of travel whereupon the discharge are is automaticallytransferred to said longer path of travel wherein it is extinguished bythe process of deionization.

5. A lightning arrester comprising a plurality of metallic electrodespositioned in spaced relationship to provide a pair of air gaps arrangedin series, and a dielectric structure formed of arc extinguishingmaterial and confining one of said air gaps, said dielectric structureincluding a pair of separate paths of travel for a discharge arebridging said confined air gap. one of said paths being shorter, morerestricted and offering less resistance to insure the initialestablishment of the discharge are in said path, and the other of saidpaths being of a predetermined greater length and unrestricted toprovide a passage in which the discharge are is extinguished, thetransfer of said initially established discharge arc being automaticallyeffected through the increased resistance to the continued flow of thedischarge are along the initially established path of travel broughtabout through the action of the discharge are upon said dielectricmaterial.

6. A lightning arrester comprising a plurality of metallic electrodespositioned in spaced relationship to provide a pair of air gaps arrangedin series, and a dielectric structure formed of arc extinguishingmaterial and confining one of said air gaps, said dielectric structurecomprising a cylindrical inner member, a tubular outer member, and anintermediate member disposed between the adjacent surfaces of said innerand outer members and between the adjacent portions of said electrodesforming said confined air gap, said intermediate member cooperating withthe adjacent surface of said inner and outer members to delineate aplurality of paths of travel for a discharge arc bridging the confinedair gap, one of said paths being shorter than another and offering lessresistance to insure the initial establishment of the discharge aretherealong, another of said paths having a predetermined lengthsubstantially greater than said shorter path and forming an unrestrictedpassage in which the discharge are is extinguished by the process ofdeionization, the establishment of the discharge are along said shorterpath effecting the automatic transfer of the discharge are to saidlonger path through the marked increase in resistance to the continuedflow of the discharge are along the initially established path of travelbrought about through the action of the discharge arc upon saiddielectric structure.

'7. A lightning arrester constructed as set forth in claim 6, in whichthe intermediate member of the dielectric structure is helical in form.

8. A lightning arrester constructed as set forth in claim 6, in whichthe intermediate member of the dielectric structure forms the means forrestricting the shorter path of travel for the discharge arc.

9. A lightning arrester comprising a hollow insulator body forming ahousing for a plurality of metallic electrodes positioned in spacedrelationship to provide a pair of air'gaps arranged in series, and adielectric structure formed of arc extinguishing material and confiningone of said air gaps, said dielectric structure including a pair ofseparate paths of travel for a discharge are between said electrodesformin said confined air gap, one of said paths being shorter, partiallyrestricted and ofiering less resistance to insure the initialestablishment of the discharge are along its path, the other of saidpaths being of a predetermined length substantially greater than saidshorter path and providing a passage in which the discharge are isextinguished by the process of deionization, the establishment of thedischarge are along said shorter path effecting the automatic transferof the discharge are to said longer path through the increasedresistance to its continued flow along the initially established pathresulting from the action of the discharge are upon said dielectricstructure, which resistance reaches a magnitude greater than theresistance offered by said longer path thereby causing the transfer ofthe discharge are to said longer path wherein it is extinguished, andventing means for relieving internal pressure caused by the dischargearc.

10. A lightning arrester constructed as set forth in claim 9 in whichthe dielectric structure comprises a plurality of telescopicallyarranged members.

11. A lightning arrester constructed as set forth in claim 9 in whichthe longer path of travel for the discharge are is in the form of atortuous passage.

12. A lightning arerster comprising a hollow insulator body forming ahousing for a plurality of metallic electrodes positioned in spacedrelationship to provide a pair of air gaps arranged in series, and adielectric structure formed of arc extinguishing material and confiningone of said air gaps, said dielectric structure comprising a pluralityof members having adjacent cooperating surfaces, one of said membershaving a relatively smooth surface and another having a convolutedsurface cooperating with said smooth w surface to delineate a tortuousair passage forming a path of travel for a discharge are bridging saidconfined air gap, said smooth surface on one of said members forming ashorter path of travel for the discharge are to insure its initialestablishment along said shorter path, the resistance to continuedtravel of the discharge are along said initially established path beingsubstantially increased immediately upon the establishment of thedischarge are through the action of the are upon the dielectricstructure, the resistance thus produced attaining a magnitude greaterthan the resistance offered by said tortuous air passage to effect thetransfer of the discharge are to said tortuous passage wherein it isextinguished by the process of deionization, and venting means forrelieving internal pressure evolved during the presence of the dischargeare.

13. A lightning arrester constructed as set forth in claim 12 in whichthe dielectric structure comprises a pair of telescopically arrangedmembers.

14. A lightning arrester constructed as set forth in claim 12 in whichthe dielectric structure comprises a pair of telescopically arrangedmembers having, respectively, smooth and convoluted surfaces cooperatingto provide separate paths of travel for a discharge are.

ROLLAND D. NELSON. EDWIN A. LINK.

REFERENCES CITED The following references are of record in the file ofthis patent:

Pittman Dec. '7, 1943

